Tourmaline crystal transducer



SQPi 5, 1950 E. KLEIN 2,-52,938

TOURMALINE CRYSTAL TRANSDUCER Filed Oct. 7, 1944 2 Sheets-Sheet 1 apt. 5, W50 E. KLEIN 0, 38

TOURMALINE CRYSTAL TRANSDUCER Filed Oct. 7, 1944 2 Sheets-Sheet 2 gywem m ELIAS KLEIN Patented Sept. 5, 1 950 TOURMALINE CRYSTAL TRANSDUCER Elias Klein, Washington, D. 0.

Application October 7, 1944, Serial N0. 557,715

3 Claims. (Cl. 177386) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The present invention relates in general to hydrophones and more particularly to a hydrophone for use as a standard in under-water measurement of sound intensities.

A prime object of the invention is the provision of a standard hydrophone which shall be stable in its sensitivity and capable of affording reproduction of substantially identical indications upon its application to the measurement of identical forces at different times.

Another object is the provision of a structure particularly adapted to the use of tourmaline crystal as a piezoelectric transducing substance.

Another object is the provision of a hydrophone structure which shall be physically sturdy and durable and capable of being readily disassembled or partly disassembled for inspection or repair.

Various other objects and advantages of the invention will become apparent from a perusal of the following specification and the drawings accompanying the same.

In the drawings:

Fig. 1 is an axial cross sectional view of the hydrophone.

Fig. 2 is a fragmentary sectional View of a portion of the crystal pile taken in the same plane as Fig. 1 but on a greatly enlarged scale.

Fig. 3 is a fragmentary side View of the crystal stack looking from the bottom of Fig. 1.

Fig. 4 is a front-end view of the crystal stack partly broken away and looking from the left in Fig. 1.

Fig. 5 is a top-side view of the stack as positioned in Fig. 1.

Referring more particularly to the drawings, the transducer unit It is of the piezo-electric type and is built up of a plurality of relatively thin slabs or disks H to M of tourmaline crystal, which may be not substantially over one eighth of an inch thick, stacked one upon the other with like poles adjacent, and an end and intermediate electrodes IE to H3 and inertia back-plate l9 connecting the poles in multiple-aid in a manner to be later described. The back plate l9 preferably is of steel, and in the present embodimentis about of an inch thick and of the same diameter as the crystal disks. The disks are cut from tourmaline crystal each with the piezoelectric axis normal to the plane of the disk, and may be composed of a single solid slab or plate of the crystal material or may be a mosaic of several pieces fitted together in known manner as indicated by the lines of separation in the disks in Fig. 1, and the transverse lines in Fig. 4. Each at 24 in Fig. 2.

2. V disk, which as indicated in the drawings has a width several times its thickness, is provided on its opposite faces with a thin metallic coating 20, Figs. 2 and 4, preferably gold, which may be applied in any known or other suitable manner as by sputtering. The electrodes l5 to l8 are disks of sheet metal, in the presentembodiment nickel, of about .005 of an inch thick, each provided with a terminal tab such as 3land 38 for electrical connection. A disk 22 of sheet natural cork or other suitable sound insulating material covers the rear side of the back plate IS. The

assemblage consisting of the stack of crystal disks I I to M with the electrodes IE to It and the back plate [9 and cork disk 22 is cemented together under pressure by a suitable strong cement 23, such as "vulcalock, a vulcanizing or heat setting rubber cement, the cement extending between the adjoining surfaces of gold plated crystal disks, the electrodes IE to IS, the backing plate [9 and cork disk 22. The same cement material is used to fill and seal the pores of the cork disk at the surface portion. The same or other suitable cement of high insulating quality may be used for joining together the pieces of crystal to form the mosaic disks. After the parts are thus assembled with the cement in place, the stack as a Whole is baked under pressure to form a substantially solid unit. Due to slight irregularities in flatness of the electrodes [5 to I9 and the gold plated faces of the crystal disks, and the application of pressure during the cementing of the crystal stack I 0, electrical contact is established at points between the electrode disks and the gold plating on the crystal disks as indicated However such contact is not essential to operation, due to the fact that the electrical connection between the electrodes through the crystal disks is electrostatic and not conductive and that the increase in distance between the electrodes produced by the very thin layer of cement 23 is negligible compared to the thickness of the crystal disk. .A cover band or sleeve 25 of suitable, electrical insulating material, preferably mica, is fitted tightly around the crystal stack in and disks l9 and 22, and so held by a lacing 26 of strong thin thread as indicated in Fig. 3, the holes for the lacing preferably being drilled in order to insure against fracture of the band, particularly where mica is used. A mounting base 21 of insulating material having low loss at high frequencies, preferably gray styramic, supports the crystal stack l8 and disks l9 and 22, the cork disk 22 being securely cemented to the base 21 preferably with a cement 3 such as the vulcalock above mentioned. The insulating base 21 is bolted to a steel attaching disk 28 by means of bolts 29 through an intervening sound insulating disk 30 of sheet, natural cork. At the back of the attaching disk 28 is mounted a sandwich packing consisting of a steel pressure'clisk 3 lzbol-tedto the disk 2 8'by means of bolts 32 and'33 with an intervening packing disk 34 of soft, live rubber. Arrangement of the crystal disks with like polar faces juxtaposed makes possible the use of a common electrode fora pair of adjacent polar surfaces. This makes alternate electrodes opposite in polarity so that the'fe'lectrodes l5, H and I9 are of one polarity, while the electrodes I6 and [8 are of the other polarity.

To connect the various crystal elements or disks of the stack in multiple aid, the alternate electrodes l5, l1 and back plate i'9.are electrically connected together and to a terminal tab 35 through a suitable flexible conductor strip 36 as shown in Fig. 3 but omitted from Fig. 1 for the sakeof clearness. The conductor 36 is connected withthe electrodes and l! by soldering to the tabs 37 and '33 extending integrally from the electrodes through suitable openings or slots in the mica sleeve such as indicated at39 in' Fig. 2, the terminal tabs 31 and 38 being bent to lie flat over the mica sleeve as shown in Fig. 1. Connecticn of the conductor strip with the back plate 1'9 is made at the head of the terminal screw Ail threaded into theback plate as shown in Fig. 1. The terminal tab 55 is grounded to the steel attachin plate 28 through contact therewith and with the lower clamping bolt 29 which passes through the ta'binto threaded engagement with the attaching plate. Sin'iilarly the other group of alternate electrodes 16 and I8 are connected together and'to the end of an ungrounded output conductor il through a flexible conductor strip '32, shown in Fig. 5, but omitted from Fig. l for the sake of clearness. The output conductor 4| which constitutes the inner conductor of a twoconductor concentric cable 13 passes out of the transducer unit by way of the radial bore 44 and central here 4.5 passing uncovered through the bore 54, and retaining the inner cover 46 through the bore 65. Outside of the unit the inner conductor and covering enter the outer conductor 47 and covering 48 near which juncture the outer conductor is electrically connected through conducting strip 49 to the grounded pressure disk 3! which latter is in electrical connection with the grounded attaching disk 28 through bolts 32 and 33, and the inner housing 50. To seal the opening made in the outer cable covering for connection .of the jumper strip 59, this region is thoroughly taped with a sealing tape 5| of any known or other suitable kind such as splicing tape.

The transducer unit thus assembled and connected is mounted within the inner housing 50 and held therein by threaded engagement of the attaching plate 2!; with the internally threaded portion 5-2 of the housing. This places the transducer unit with the outer end facing an opening 53 in the housing closed by a sound-window element 54 of suitable sound transparent material such as liver rubber. This window element, as shown in Fig. l, is formed with a cylindrical side wall extending into the inner casing 50 in contact with the inner cylindrical wall of the casing and surrounding and spaced from the transducer unit. The window element 54 is securely joined to the inner casing 50 throughout the .75 thereon or therefor. v

4 area of contact between the two, preferably by the vulcanizing of the Window element.

To seal off the space between the inner casing 55 and the transducer unit, the pressure disk 3| is clamped against the live rubber disk 34 to expand the latter radially outwardly against the sidewall of the inner casin and inwardly against the sides of the inner cable-covering 46.

The space thus sealed 01f is filled with a liquid of substantially the same acoustical characteristics as water, preferably castor oil substantially free of air and 'moisture. Filling is effected through aaibore 55 in the bolt 33 arranged to be sealed oif by a cap-56 threaded on to the end of the hollow bolt.

The assemblage of transducer and inner casing is mounted in a relatively massive, thick-walled, outer, spherical casing 51, preferably of bronze or the like, with theouter spherical surface portion of the window 54 and -inner casing 50 forming a continuation of the'zspherical contour of the outer casing. A hermetically'sealed juncture between the "inner :casingiiiil and :the outer casing 51 is provided by the annular ridgeelement. 58, on the inner facei'ofthesflange 5'9 ofxth zinner casing, interfitting with i-the .ann'ular trough 60 in the rim of theopen ingtinthe outer casing, the troughcontaining apa'cking ring'fil of live rubber. Cap screws fizpa'ssing through openings in the flange '59 into Lthrea'ded engagement .with threaded bores 'fiil infthe rim portion of the outer casing, operate "to clamp .the flange-"59 in place with the packing 6! under compression.

With the device assembled as above described, the centralinsulated conductor 4| and the outer shielding conductor lTconstitutethex output conductors "of the piezo electric transducer, :the transducer terminal 35 and shielding conductor 41 being grounded to the outermetallic casing 5'1 and through the latter to the surrounding water when the :device is submerged. This ground connection may be traced from terminal tab 35 through attaching disk28 and inner casing 50 to the outer 'casing, and from the shielding conductor 41 through strip 49, pressure disk 3!, bolts 32-33, attachingdisk2-8 and inner casing to outer casing.

Because tourmaline crystal is piezo-electrically responsive to hydrostatic pressure in an enveloping liquid, the customary side insulation against sound for the crystal unit is purposely avoided. The soft rubber window '54, which forms a section of the wall of the inner chamber, beinghighly transparent to sound, permits sound-Waves freely to enter the oil enveloping the crystal stack and therethrough to act upon the stack for transformation into electrical energy.

While only one specific embodiment of the invention is herein shown'and described forthe sake of disclosure, it is to be understood that the invention is not limited to such specific embodiment but contemplates all such modifications and variants thereof as fall fairly within the scope and purview of the appended claims. An embodiment of the invention having the dimen sions and relative proportions above described, and shown in the drawings, will respond effectively to frequencies in the order of 8 to kilocycles per second.

The invention describedherein maybe manufactured and used by or for the Government of the United States of America for-governmental purposes without the payment of any royalties What is claimed is:

1. A transducer comprising a plurality of tourmaline-crystal plates each having a width several times its thickness, a plurality of electrode plates, said crystal plates being provided with metallic coatings on each side and stacked one upon the other with one of said electrode plates interposed between each pair of adjacent crystal plates, an electrode plate covering the outer surface of one of the end crystal plates of the stack, an electrically conducting, inertia plate covering the outer surface of the other end crystal plate, all of said plates cemented each to the other into a substantially solid, straight-sided stack by a cement extending between adjacent surfaces of said plates with points of electrical contact established between the electrode plates and adjacent metallic coatings on the crystal plates, a relatively thin band of electrical insulating material tightly secured about the sides of the said straight-sided stack and terminal leads extending from said conducting plates through and along the outside of said band.

2. A piezo-electrie transducer comprising a plurality of plates of piezo-electric crystal stacked one upon the other with like pole adjacent, a plurality of electrodes interposed one between each adjacent pair of plates, a pair of end elec trodes one adjacent the outer surface of each end plate, one of said end electrodes constituting an inertia back-plate, a plate of sound-insulating material adjacent the side of the said inertia back-plate remote from the crystal plates, means cementing said plates and electrodes into a substantially solid composite block, a pair of electrical terminals, means connecting one of said terminals with electrodes adjacent crystal plate surfaces of one polarity and means connecting the other terminal with electrodes adjacent crystal plate surfaces or the other polarity.

3. A piezo-electric transducer comprising a plurality of plates of piezo-electric crystal stacked one upon the other with like poles adjacent, a plurality of electrodes interposed one between each adjacent pair of plates, a pair of end electrodes one adjacent the outer surface of each end plate, one of said end electrodes constituting an inertia back-plate, a plate of sound-insulating material adjacent the side of the said back-plate remote from the crystal plates, said plates and electrodes being substantially coextensive in area and of like contour, means cementing said plates and electrodes into a substantially solid composite block and sealing the surface of said soundinsulating plate, a covering of electrical insulating, sound transparent, material overlying the sides of said composite block, a pair of electrical terminals, means connecting one of said terminals with electrodes adjacent crystal plate surfaces of one polarity, other connecting means connecting the other terminal with electrodes adjacent crystal plate surfaces of the other polarity, said connecting means lying outside of said coverings.

ELIAS KLEIN.

REFERENCES CITED The following references are of record in the file of this patent:

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